Jessica Meeuwig, University of Western Australia

One of the most common justifications for Western Australia’s shark cull is the longstanding use of baited hooks - or drum lines - in regions such as Queensland.

Two key questions need answering. First, is there clear evidence that drum lines reduce the number of human fatalities from sharks? And second, what is their cost in terms of killing marine wildlife?

To that end, I have analysed publicly available figures for human fatalities in Queensland with data on the program’s shark catch, to provide an assessment of its effectiveness.

Surfers, scientists and conservationists join members of the general public in gathering at Manly beach to denounce the Western Australian Government's new policy to catch and kill sharks. Photo: Damian Shaw

Over more than half a century, the program has taken a large toll on wildlife, while any increase in human safety has been equivocal at best.

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The Queensland cull

As of December 2013, there were 369 drum lines and 30 nets deployed off the Queensland coast, mostly near swimming beaches. The program has grown steadily since it began in April 1962 with the deployment of 24 drum lines on the Gold Coast; it now extends to Cairns across a total of ten regional areas.

Between 1853 and 2013 there were at least 71 human fatalities due to unprovoked shark attacks in Queensland, with the majority of these attributed to tiger sharks and only a single fatality to white sharks.

During these 160 years, the average fatality rate varied. From 1850 to 1910 it was 0.32 fatalities per year, but then a spike in fatalities in the 1920s saw the average increase to 1.1 per year. After that, the rate of fatal attacks generally declined, falling to a low of 0.2 per year in the 1990s. Since 1962, when the drum line program began, the fatality rate has averaged 0.37 per year, a number not significantly different than that previous to the 1920s.

The graph shows that there has been a significant decline in Queensland’s rate of shark attack fatalities but that it started 40 years before drum lines were first deployed. There has been no further reduction in fatalities since the program began, despite half a century of increasing drum line deployments.

Note also that these statistics include fatalities in areas with and without drum lines. Of the 71 reported Queensland fatalities, 50 were in areas such as the outer Great Barrier Reef or Moreton Bay, where no drum lines (or nets) are present.

In areas without drum lines, the average fatality rate, calculated on a decadal basis, was 0.34 per year before 1970 (used as a cut off point given the 1960s saw only relatively few drum limes compared to the full program now implemented) and 0.24 afterwards. Even without drum lines, fatalities declined by 28per cent between these two periods.

In areas with drum lines, fatality rates fell from 0.05 to 0.02 fatalities per year pre- and post installation of the drum lines, a decline of 70 per cent. This suggests that the fatality rate fell more rapidly in areas with drum lines than those without.

However, this result is deceptive. Of the seven locations with drum lines only (no nets), six had recorded only a single fatal attack prior to the installation of drum lines (ranging from 5 to 95 years before the lines were deployed). Only Kissing Point had a history of more than one fatality (in 1916, 1933 and 1955) before drum lines were installed in 1965. So for the most part, this apparently rapid decline represents the difference between one attack that could have occurred up to 95 years ago, and no attacks today at a limited number of sites.

This highlights the problems we face when trying to understand patterns in shark attacks and the effect of mitigation programs – fatalities are such rare events that differentiating between random coincidence and underlying patterns is fraught with difficulty.

What is the cost to marine life?

In contrast to their contribution to human safety, one thing we can be certain of is drum lines' ecological cost. The most recent available data show that Queensland caught some 6250 sharks on drum lines between 2001 and 2013, or an average of 480 animals per year.

This catch included 35 different species, the most common being tiger sharks (41 per cent), bull sharks (17 per cent) and black tip reef whalers (12 per cent). White sharks, although considered a key target species in WA, represent less than 1 per cent of the Queensland catch with about five caught per year.

Only 3 per cent of the sharks killed on Queensland drum lines are considered not to be at conservation risk. According to the International Union for Conservation of Nature, four species, representing 5.2 per cent of the catch, are “endangered”; nine species (9.6 per cent of the catch) are "vulnerable”; and 15 species (80.6per cent) are classed as “near threatened”. Only six species (1per cent) are considered to be of “least concern”, while one species (2per cent) is considered “data deficient”.

Sharks longer than 3 metres have been classified as dangerous to humans, at least in WA. Yet only 11per cent of the animals culled in Queensland were larger than this – the average size of sharks captured on the drum lines was 1.9 metres.

In terms of reproductive maturity, all of the white sharks and most of the tiger and bull sharks that were caught were juveniles. As a key strategy for shark recovery is the protection of large breeding individuals, this may appear a reasonable outcome. But equally, juvenile deaths will ultimately reduce the future population of breeding adults.

What have we learned?

Based on this analysis, we can conclude that:

Shark-related fatalities in Queensland have declined in both areas with and without drum lines, with the steepest rates of decline before their installation.

The effectiveness of drum lines is difficult to evaluate, as the rates of attacks before and after their deployment are both very low. Moreover, 83per cent of drum lines are deployed at locations where a fatal attack has never occurred.

The ecological cost of drum lines is high, with 97per cent of sharks caught since 2001 considered to be at some level of conservation risk, and 89per cent caught in areas where no fatalities have occurred.

Drum lines: a blunt tool

It could be argued that the drum line program in Queensland is justified simply because it may remove sharks from popular areas. However, it is a very blunt tool and ignores the important ecological roles that sharks play in our oceans.

Moreover, its success in reducing human fatalities is hard to validate. The decreases may simply reflect broader declines in shark populations, driving down encounter rates despite the increased human presence in the ocean. Or they may simply be random.

There are non-lethal techniques that can potentially achieve much better outcomes. Humans and sharks alike could benefit from an approach that embraces new ideas, rather than one that has produced little measurable effect in half a century, other than to kill threatened species.

Jessica Meeuwig does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

27 comments

Sharks are so important for the health of the ocean, it's bizarre in this day and age that this is still going on.

The worse part is that the oceans are losing 200,000 a day to Asian prevalence for shark fin soup, we are very close to a massive shift in the hierarchy of the oceans.

Commenter

JoBlo

Location

Here

Date and time

February 21, 2014, 6:06PM

What about the Caucasian prevalence for flake?

Commenter

Steve

Date and time

February 22, 2014, 12:01PM

hunt is about to allow the Magris back and he "promised" to repeal marine park status.The anti environment Minister at work will ensure our oceans are unbalanced.

Commenter

A country gal

Date and time

February 22, 2014, 1:57PM

This analysis is fatuous at best.

The author fails to consider the increasing density of swimmers on Queensland beaches since the shark control programme. He looks merely at fatalities per year, not fatalities per year be thousand (or ten thousand) swimmers. Viewed in this context, the rate continues to drop.

The number of swimmers is a critical statistical value, and to omitting it is either strangely incompetent, or else reeks of trying to fit the data to a pre-determined point of view.

Commenter

Peregrine

Location

Brisbane

Date and time

February 21, 2014, 6:49PM

@ Peregrine, number of swimmers is a critical number but we don't have enough historical data to know how that has shifted with direct regard to shark attacks.

What you fail to account for as well is over fishing of our waters (moving sharks closer to the shoreline) and more importantly, the overfishing of the shark population. I'm terrified of sharks and don't believe for a second that drumlines do anything more than draw them in.

What I'm saying is that there are better ways to deal with this and we're not using them.

Commenter

JoBlo

Location

Here

Date and time

February 21, 2014, 7:13PM

"The decreases may simply reflect broader declines in shark populations, driving down encounter rates despite the increased human presence in the ocean."

Or they might not.

"From 1850 to 1910 it was 0.32 fatalities per year, but then a spike in fatalities in the 1920s saw the average increase to 1.1 per year. After that, the rate of fatal attacks generally declined, falling to a low of 0.2 per year in the 1990s. Since 1962, when the drum line program began, the fatality rate has averaged 0.37 per year, a number not significantly different than that previous to the 1920s."

Actually not so difficult to explain.

Hardly anyone swam in the open ocean prior to the 1920's. In fact, it was illegal to do so during daylight hours until 1903 and even then not on Sundays, Christmas or Easter breaks.

So basically only Saturdays for surfing. Not much human exposure to sharks then.

Surf lifesaving commenced after 1903 in response to the increasing number of now legal bathers, peaking in the 1920's when it became very fashionable to swim in the sea.

The mortality rate correlates directly with the increasing popularity of beach bathing dating from the 1920's. The subsequent drop in fatalities can readily be attributed to the warning systems put in place such as shark bells which removed people from the water before attacks occurred.

Following WW2, surfing’s popularity rose again - especially boardriding to which higher mortality rates can be attributed.

This was again mitigated against however, with better beach patrol protocols - and the introduction of drum lines in the 1960's.

You could equally argue that without the drum lines the number of attacks would have been higher.

So then, it’s not all about the marine science. There are strong social factors also at play.

Commenter

PJ

Location

Brisbane

Date and time

February 21, 2014, 9:28PM

+1. The number of swimmers is of course essential. Also, a break down of different regions, drum lined and not. And if the number of fatalities is too low to measure, what about the number of serious attacks. How many sharks have been counted. What about the fish supply?

Unfortunately, serious analysis has no place in public policy. What counts are the emotional arguments of save the shark vs make the sea safe for our children.

But it would seem common sense that any over population of sharks might encourage them to look for alternate food sources. Whereas natural selection will tend to produce sharks that avoid areas near the drum lines, i.e. the beaches.

Commenter

T.

Date and time

February 22, 2014, 10:50AM

T is absolutely correct, and brings a degree of analysis that shames the original author.

That this original piece passes for an academic paper just leaves me dumbfounded.

Commenter

Peregrine

Date and time

February 22, 2014, 3:43PM

The graphs do show a decline in shark deaths. But that started after aircraft were used just after the war. The Gold and Sunshine coasts would be bereft of surfers if drumlines were stopped. The average person is not interested in statements about vulnerable or protected sharks when the experts themselves can't tell how many there are. Otherwise why ask for research funding in that direction? Human life is more important than sharks and an opposite view is weird. Humans have the right to all environments and if anyone thinks otherwise I say too bad, how sad.

Commenter

bookim

Date and time

February 21, 2014, 6:55PM

@ bookim, so you're saying that humans can slaughter all species to enable their own survival any time they want, rather than finding a way to co-exist. That's nothing short of mentally deficient thinking. There are other ways.

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